Compositions, polymers, and laminates

Abstract

The present invention provides a composition that can easily coat separators for electrochemical devices, form a coating with excellent electrolyte resistance, and improve the heat shrinkage resistance of the resulting separator. [Solution] A composition for coating a separator for an electrochemical device is provided, wherein the composition contains a polymer containing trifluoroethylene units, the trifluoroethylene unit content of the polymer is 57 to 100 mol% of the total monomer units, and if the polymer contains monomer units other than trifluoroethylene units, the other monomers include tetrafluoroethylene, or at least one monomer (α) selected from the group consisting of tetrafluoroethylene and fluorinated monomers (excluding trifluoroethylene and tetrafluoroethylene) and polar group-containing monomers.

Description

[Technical Field]

[0001] This disclosure relates to compositions for coating separators for electrochemical devices, separators for electrochemical devices, electrochemical devices, lithium-ion secondary batteries, polymers, and laminates. [Background technology]

[0002] Patent Document 1 describes the use of a heat-resistant fluorinated copolymer based on trifluoroethylene (VF3) and tetrafluoroethylene (C2F4) as a substrate coating material and / or an ultra-flexible material.

[0003] Patent Document 2 describes an inorganic composite porous separator film comprising (a) a polyolefin-based separator film substrate and (b) an active layer coated with a mixture of inorganic particles and a binder polymer on one or more regions selected from the group consisting of the surface of the substrate and a part of the pores present on the substrate, wherein the active layer is characterized in that the inorganic particles are bound together by the binder polymer and a pore structure is formed by the gaps between the inorganic particles. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-231645 [Patent Document 2] Special Publication No. 2008-524824 [Overview of the project] [Problems that the invention aims to solve]

[0005] The present disclosure aims to provide a composition for coating separators for electrochemical devices, which can easily coat separators, form a coating with excellent electrolyte resistance, and improve the heat shrinkage resistance of the resulting separator. Furthermore, this disclosure aims to provide a polymer that can form a coating with excellent electrolyte resistance and can improve the heat shrinkage resistance of a separator. Furthermore, this disclosure aims to provide a laminate that can be manufactured with high productivity, has a coating layer with excellent electrolyte resistance, and has excellent heat shrinkage resistance. [Means for solving the problem]

[0006] According to this disclosure, a composition for coating a separator for an electrochemical device is provided, wherein the composition contains a polymer containing trifluoroethylene units, the trifluoroethylene unit content of the polymer is 57 to 100 mol% of the total monomer units, and if the polymer contains other monomer units other than trifluoroethylene units, the other monomers include tetrafluoroethylene, or at least one monomer (α) selected from the group consisting of tetrafluoroethylene and fluorinated monomers (excluding trifluoroethylene and tetrafluoroethylene) and polar group-containing monomers.

[0007] In the compositions of this disclosure, it is preferable that the fluorinated monomer is at least one selected from the group consisting of chlorotrifluoroethylene, 2,3,3,3-tetrafluoropropene, hexafluoropropylene, and fluoroalkyl vinyl ethers. In the compositions of the present disclosure, it is preferable that the polar group-containing monomer is at least one selected from the group consisting of (meth)acrylic acid, 3-butenoic acid, 4-pentenoic acid, 2-carboxyethyl acrylate, hydroxyethyl acrylate, 2-hydroxypropyl acrylate, acryloyloxyethyl succinic acid, and salts thereof. In the compositions of the present disclosure, it is preferable that the polymer is at least one selected from the group consisting of polymers containing only trifluoroethylene units and tetrafluoroethylene units, and polymers containing trifluoroethylene units, tetrafluoroethylene units, and monomer (α) units. In the composition of the present disclosure, it is preferable that the total content of trifluoroethylene units and tetrafluoroethylene units of the polymer is 90 to 100 mol% relative to the total monomer units, and the content of monomer (α) units is 10 to 0 mol% relative to the total monomer units. In the compositions of this disclosure, it is preferable that the polymer does not contain vinylidene fluoride units. The compositions of this disclosure preferably further contain a solvent.

[0008] Furthermore, this disclosure provides a separator for an electrochemical device comprising a substrate and a coating layer formed from the above composition.

[0009] In the separator for electrochemical devices of this disclosure, it is preferable that the substrate is formed from an organic material.

[0010] Furthermore, this disclosure provides an electrochemical device comprising the above-mentioned separator for electrochemical devices.

[0011] Furthermore, this disclosure provides a lithium-ion secondary battery comprising the above-mentioned separator for electrochemical devices.

[0012] Furthermore, the present disclosure provides a polymer containing trifluoroethylene units, tetrafluoroethylene units, and monomer (α) units, wherein monomer (α) is at least one selected from the group consisting of fluorinated monomers (excluding trifluoroethylene and tetrafluoroethylene) and polar group-containing monomers.

[0013] In the polymers of this disclosure, it is preferable that the content of trifluoroethylene units in the polymer is 57 to 99 mol% relative to the total monomer units. In the polymer of this disclosure, it is preferable that the total content of trifluoroethylene units and tetrafluoroethylene units of the polymer is 90 to 99.99 mol% of the total monomer units, and the content of monomer (α) units is 10 to 0.01 mol of the total monomer units.

[0014] Furthermore, the present disclosure provides a laminate comprising a substrate formed from an organic material and a coating layer formed from a composition, wherein the composition contains a polymer containing trifluoroethylene units, the trifluoroethylene unit content of the polymer is 57 to 100 mol% of the total monomer units, and if the polymer contains other monomer units other than trifluoroethylene units, the other monomers include at least tetrafluoroethylene, or tetrafluoroethylene and at least one monomer (α) selected from the group consisting of fluorinated monomers (excluding trifluoroethylene and tetrafluoroethylene) and polar group-containing monomers. [Effects of the Invention]

[0015] According to this disclosure, it is possible to provide a composition for coating separators for electrochemical devices that can easily coat separators, form a coating with excellent electrolyte resistance, and improve the heat shrinkage resistance of the resulting separator. Furthermore, this disclosure provides a polymer that can form a coating with excellent electrolyte resistance and can improve the heat shrinkage resistance of the separator. Furthermore, according to this disclosure, it is possible to provide a laminate that can be manufactured with high productivity, has a coating layer with excellent electrolyte resistance, and has excellent heat shrinkage resistance. [Modes for carrying out the invention]

[0016] The following describes specific embodiments of this disclosure in detail, but this disclosure is not limited to the embodiments described below.

[0017] The basic structure of a lithium-ion secondary battery consists of a non-aqueous electrolyte placed between the positive and negative electrodes, with a separator in between if necessary. The separator is interposed between the positive and negative electrodes to prevent contact between the active materials of both electrodes, and forms a passage for ion conduction between the electrodes by allowing the electrolyte to flow through its pores. Furthermore, the separator is required to have a shutdown function that prevents excessive current by interrupting the current flow in the battery due to causes such as a short circuit between the positive and negative electrodes. The separator shuts down by closing its microporous membrane when the normal operating temperature of the battery is exceeded.

[0018] Conventionally, porous membranes such as microporous polyolefin films made of polyethylene, polypropylene, etc., have been commonly used as separators. However, these polyolefin-based porous membranes have high thermal shrinkage properties, resulting in poor dimensional stability at high temperatures. If the pores in the separator become blocked due to abnormal heating of a lithium-ion secondary battery, and the internal temperature of the battery continues to rise, there is a risk that the separator will shrink and break, causing an internal short circuit and potentially leading to fire. To improve the safety of batteries under these high-temperature conditions, there is a need to improve the heat shrinkage resistance of separators.

[0019] Furthermore, as described in Patent Document 2, when using a technique for coating the separator, there is a need for a technique that can easily coat the separator and form a coating with excellent electrolyte resistance so that the coating does not swell or dissolve even when in contact with the electrolyte used in lithium-ion secondary batteries.

[0020] Through diligent research, the inventors discovered that by appropriately selecting the monomer composition of a polymer, the polymer can be sufficiently dissolved in a solvent such as N-methyl-2-pyrrolidone to prepare a composition with appropriate viscosity. Furthermore, by using a polymer with an appropriately selected monomer composition, a coating with excellent electrolyte resistance can be formed, thereby improving the heat shrinkage resistance of the resulting separator.

[0021] In other words, the composition of the present disclosure is a composition for coating separators for electrochemical devices, and contains a polymer having a specific monomer composition. By using the composition of the present disclosure, separators can be easily coated, a coating with excellent electrolyte resistance can be formed, and the heat shrinkage resistance of the resulting separator can be improved.

[0022] (polymer) The compositions of this disclosure contain polymers containing trifluoroethylene units.

[0023] The polymer described above may be a homopolymer containing only trifluoroethylene units, or a copolymer containing trifluoroethylene units and other monomer units other than trifluoroethylene units. The compositions of this disclosure may contain one or more polymers containing trifluoroethylene units.

[0024] The trifluoroethylene unit content in the above polymer is 57 to 100 mol%, preferably 60 mol% or more, more preferably 62 mol% or more, even more preferably 65 mol% or more, preferably 99 mol% or less, and more preferably 98 mol% or less, relative to the total monomer units. By setting the trifluoroethylene unit content to 62 mol% or more, preferably 65 mol% or more, the heat shrinkage resistance of the separator is further improved.

[0025] The content of other monomer units in the above polymer is preferably 0 to 43 mol%, more preferably 40 mol% or less, even more preferably 38 mol% or less, particularly preferably 35 mol% or less, more preferably 1 mol% or more, and even more preferably 2 mol% or more, relative to the total monomer units.

[0026] If the polymer contains other monomer units, these other monomers may be fluorinated monomers or non-fluorinated monomers. If the polymer used in the composition of this disclosure contains other monomer units, these other monomers must contain at least tetrafluoroethylene, or tetrafluoroethylene and at least one monomer (α) selected from the group consisting of fluorinated monomers (excluding trifluoroethylene and tetrafluoroethylene) and polar group-containing monomers. In this way, by using a polymer containing tetrafluoroethylene (TFE) units as other monomer units along with trifluoroethylene units, a coating with even better electrolyte resistance can be formed, and the heat shrinkage resistance of the resulting separator can be further improved.

[0027] As the polymer, at least one selected from the group consisting of polymers containing only trifluoroethylene units and tetrafluoroethylene units, and polymers containing trifluoroethylene units, tetrafluoroethylene units, and monomer (α) units is preferred.

[0028] The content of tetrafluoroethylene units in the above polymer is preferably 0 to 43 mol%, more preferably 40 mol% or less, even more preferably 38 mol% or less, particularly preferably 35 mol% or less, more preferably 1 mol% or more, and even more preferably 2 mol% or more, relative to the total monomer units.

[0029] When the polymer contains trifluoroethylene units and tetrafluoroethylene units, it is preferable that the total content of trifluoroethylene units and tetrafluoroethylene units in the polymer is 90 to 100 mol% relative to the total monomer units, and the content of monomer (α) units is 10 to 0 mol% relative to the total monomer units.

[0030] The total content of trifluoroethylene units and tetrafluoroethylene units is more preferably 90 to 99.99 mol%, even more preferably 92 mol% or more, particularly preferably 94 mol% or more, even more preferably 99 mol% or less, and particularly preferably 98 mol% or less.

[0031] The monomer (α) unit content is more preferably 10 to 0.01 moles, even more preferably 8 mol% or less, particularly preferably 6 mol% or less, even more preferably 1 mol% or more, and particularly preferably 2 mol% or more.

[0032] Examples of fluorinated monomers (excluding trifluoroethylene and tetrafluoroethylene) include vinylidene fluoride (VdF), vinyl fluoride, chlorotrifluoroethylene (CTFE), fluoroalkyl vinyl ether, hexafluoropropylene (HFP), (perfluoroalkyl)ethylene, 2,3,3,3-tetrafluoropropene, and trans-1,3,3,3-tetrafluoropropene.

[0033] As the fluoroalkyl vinyl ether, a fluoroalkyl vinyl ether having a fluoroalkyl group with 1 to 5 carbon atoms is preferred, and at least one selected from the group consisting of perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether), and perfluoro(propyl vinyl ether) is more preferred.

[0034] As the fluorinated monomer, at least one selected from the group consisting of VdF, CTFE, 2,3,3,3-tetrafluoropropene, HFP, and fluoroalkyl vinyl ether is preferred, and at least one selected from the group consisting of CTFE, 2,3,3,3-tetrafluoropropene, HFP, and fluoroalkyl vinyl ether is more preferred.

[0035] The fluorinated monomer may or may not have a polar group. A fluorinated monomer having a polar group may be used as the fluorinated monomer.

[0036] The VdF unit content in the above polymer is preferably low, as this allows for the formation of a coating with even better electrolyte resistance. The VdF unit content in the above polymer is preferably less than 40 mol%, more preferably less than 30 mol%, even more preferably less than 20 mol%, particularly preferably less than 10 mol%, preferably 0 mol% or more, and more preferably 1 mol% or more, relative to the total monomer units. It is also preferable that the above polymer does not contain VdF units.

[0037] Examples of non-fluorinated monomers include non-fluorinated monomers without polar groups, such as ethylene and propylene, and non-fluorinated monomers with polar groups. Hereinafter, fluorinated monomers with polar groups and non-fluorinated monomers with polar groups may be collectively referred to as polar group-containing monomers.

[0038] If a monomer having a polar group is used as another monomer, the polar group is introduced into the polymer, thereby providing excellent adhesion between the substrate and the coating layer. As the polar group, at least one selected from the group consisting of carbonyl group-containing groups, epoxy groups, hydroxyl groups, sulfonic acid groups, sulfate groups, phosphoric acid groups, amino groups, amide groups, and alkoxy groups is preferred, at least one selected from the group consisting of carbonyl group-containing groups, epoxy groups, and hydroxyl groups is more preferred, and a carbonyl group-containing group is even more preferred. The above hydroxyl group does not include hydroxyl groups that constitute part of the above carbonyl group-containing group. Furthermore, the above amino group is a monovalent functional group obtained by removing hydrogen from ammonia, a primary or secondary amine.

[0039] The carbonyl group-containing group mentioned above is a functional group having a carbonyl group (-C(=O)-). The carbonyl group-containing group is preferably a group represented by the general formula: -COOR (where R represents a hydrogen atom, an alkyl group, or a hydroxyalkyl group) or a carboxylic acid anhydride group, and more preferably a group represented by the general formula: -COOR. The number of carbon atoms in the alkyl group and hydroxyalkyl group is preferably 1 to 16, more preferably 1 to 6, and even more preferably 1 to 3. Specific examples of groups represented by the general formula: -COOR include -COOCH2CH2OH, -COOCH2CH(CH3)OH, -COOCH(CH3)CH2OH, -COOH, -COOCH3, -COOC2H5, etc. If the group represented by the general formula: -COOR is -COOH or contains -COOH, then -COOH may be a carboxylate salt such as a metal carboxylate salt or an ammonium carboxylate salt.

[0040] Furthermore, the carbonyl group-containing group may also be a group represented by the general formula: -X-COOR (where X is an atomic group whose main chain consists of 1 to 20 atoms and has a molecular weight of 500 or less, and R represents a hydrogen atom, an alkyl group, or a hydroxyalkyl group). The number of carbon atoms in the alkyl group and hydroxyalkyl group is preferably 1 to 16, more preferably 1 to 6, and even more preferably 1 to 3.

[0041] The amide group described above is preferably a group represented by the general formula: -CO-NRR' (where R and R' independently represent a hydrogen atom or a substituted or unsubstituted alkyl group), or a bond represented by the general formula: -CO-NR”- (where R represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted phenyl group).

[0042] The above polar group-containing monomers include hydroxyalkyl (meth)acrylates such as hydroxyethyl acrylate and 2-hydroxypropyl acrylate; alkylidenemalonate esters such as dimethyl methylidenemalonate; vinyl carboxyalkyl ethers such as vinyl carboxymethyl ether and vinyl carboxyethyl ether; carboxyalkyl (meth)acrylates such as 2-carboxyethyl acrylate and 2-carboxyethyl methacrylate; (meth)acryloyloxyalkyl dicarboxylic acid esters such as acryloyloxyethyl succinic acid, acryloyloxypropyl succinic acid, methacryloyloxyethyl succinic acid, acryloyloxyethyl phthalic acid, and methacryloyloxyethyl phthalic acid; monoesters of unsaturated dibasic acids such as monomethyl maleate, monoethyl maleate, monomethyl citraconic acid, and monoethyl citraconic acid; general formula (4): [ka] (In the formula, R 11 ~R 13 R independently represents a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms. 14 Y represents a single bond or a hydrocarbon group with 1 to 8 carbon atoms. 1 represents inorganic cations and / or organic cations. Examples include monomers represented by (4); unsaturated dibasic acids such as maleic acid, maleic anhydride, citraconic acid, and citraconic anhydride; etc.

[0043] As the polar group-containing monomer units that the polymer may contain, units based on monomer (4) represented by general formula (4) are preferred.

[0044] In general formula (4), Y 1 represents an inorganic cation and / or an organic cation. Examples of the inorganic cation include cations such as H, Li, Na, K, Mg, Ca, Al, Fe, etc. Examples of the organic cation include NH4, NH3R 15 , NH2R 15 2, NHR 15 3, NR 15 4 (R 15 independently represents an alkyl group having 1 to 4 carbon atoms.). Examples of the cation include those mentioned above. Y 1 is preferably H, Li, Na, K, Mg, Ca, Al, NH4, more preferably H, Li, Na, K, Mg, Al, NH4, still more preferably H, Li, Al, NH4, and particularly preferably H. Note that specific examples of the inorganic cation and the organic cation are described by omitting the symbols and valences for convenience.

[0045] In general formula (4), R 11 ~R 13 independently represents a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms. The hydrocarbon group is a monovalent hydrocarbon group. The number of carbon atoms of the hydrocarbon group is preferably 4 or less. Examples of the hydrocarbon group include an alkyl group, an alkenyl group, an alkynyl group, etc. having the above number of carbon atoms, and a methyl group or an ethyl group is preferred. R 11 and R 12 are preferably independently a hydrogen atom, a methyl group or an ethyl group, and R 13 is preferably a hydrogen atom or a methyl group.

[0046] In general formula (4), R 14 represents a single bond or a hydrocarbon group having 1 to 8 carbon atoms. The hydrocarbon group is a divalent hydrocarbon group. The number of carbon atoms of the hydrocarbon group is preferably 4 or less. Examples of the hydrocarbon group include an alkylene group, an alkenylene group, etc. having the above number of carbon atoms, and among them, at least one selected from the group consisting of a methylene group, an ethylene group, an ethylidene group, a propylidene group and an isopropylidene group is preferred, and a methylene group is more preferred.

[0047] The monomer (4) is preferably at least one selected from the group consisting of (meth)acrylic acid and its salts, vinylacetic acid (3-butenic acid) and its salts, 3-pentenoic acid and its salts, 4-pentenoic acid and its salts, 3-hexenoic acid and its salts, 4-heptenoic acid and its salts, and 5-hexenoic acid and its salts.

[0048] Since the above polymer provides excellent adhesion between the substrate and the coating layer, it is preferable to further contain monomer (3) units represented by general formula (3) as other monomer units.

[0049] General formula (3): [ka] (In the formula, R 5 ~R 7 R is independently H, F, CH3, or CF3, and X is an atomic group with a molecular weight of 500 or less, consisting of single bonds or a main chain with 1 to 20 atoms. OH (This is a C1-C5 hydrocarbon group containing H or at least one OH group.)

[0050] R 5 ~R 7 R is independently H, F, CH3, or CF3. 5 ~R 7 H or CH3 are preferred as the base material.

[0051] X is an atomic group with a molecular weight of 500 or less, consisting of single bonds or a main chain with 1 to 20 atoms.

[0052] The number of atoms in the main chain of the atomic group is 1 to 20, more preferably 1 to 14, even more preferably 1 to 8, and particularly preferably 1 to 7. The number of atoms in the main chain of the atomic group refers to the number of unsaturated bonds (CR). 5 R 6 =CR 7 This refers to the number of atoms in the skeletal structure of a chain that connects a carbonyl group (-C(=O)-) with the fewest possible number of atoms.

[0053] The molecular weight of the atomic group is preferably 450 or less, more preferably 390 or less, even more preferably 340 or less, preferably 14 or more, more preferably 20 or more, and even more preferably 28 or more.

[0054] As for the atomic group, a divalent group represented by one of the following formulas is preferred because it is possible to obtain an electrode mixture that is less likely to increase viscosity and a coating layer with even better adhesion to the substrate. General formula (3a):*-L 1 - (In the formula, *- represents an unsaturated bond (CR) 5 R 6 =CR 7 -) is a bonding hand that connects with L 1 (This refers to an alkylene group with 1 to 20 carbon atoms.) General formula (3b):*-CO-L 2 - (In the formula, *- represents an unsaturated bond (CR) 5 R 6 =CR 7 -) is a bonding hand that connects with L 2 (This refers to an alkylene group with 1 to 19 carbon atoms.) General formula (3c):*-OL 3 - (In the formula, *- represents an unsaturated bond (CR) 5 R 6 =CR 7 -) is a bonding hand that connects with L 3 (This refers to an alkylene group with 1 to 19 carbon atoms.) General formula (3d):*-COO-L 4 - (In the formula, *- represents an unsaturated bond (CR) 5 R 6 =CR 7 -) is a bonding hand that connects with L 4 (This refers to an alkylene group with 1 to 18 carbon atoms.) General formula (3e):*-COO-L 5 -OCO-L 6 - (In the formula, *- represents an unsaturated bond (CR) 5 R 6 =CR7 -) is a bonding hand that connects with L 5 and L 6 These are independently alkylene groups, and L 5 and L 6 The total number of carbon atoms is between 2 and 16.

[0055] The atomic group is preferably at least one selected from the group consisting of a divalent group represented by general formula (3a), a divalent group represented by general formula (3c), a divalent group represented by general formula (3d), and a divalent group represented by general formula (3e), and more preferably at least one selected from the group consisting of a divalent group represented by general formula (3c), a divalent group represented by general formula (3d), and a divalent group represented by general formula (3e).

[0056] L 1 ~L 6 Independently, alkylene groups having 1 to 10 carbon atoms are preferred, alkylene groups having 1 to 4 carbon atoms are more preferred, alkylene groups having 1 to 3 carbon atoms are even more preferred, and methylene groups or ethylene groups are particularly preferred.

[0057] R OH R is a C1-C5 hydrocarbon group containing H or at least one OH. OH H is preferred. OH When H is present, the resulting carboxyl group (-COOH) may form salts with cations such as Li, Na, K, Mg, Ca, Al, and NH4.

[0058] Examples of monomers (3) include unsaturated monocarboxylic acids having 3 to 6 carbon atoms, such as (meth)acrylic acid, vinyl acetic acid (3-butenoic acid), 3-pentenoic acid, 4-pentenoic acid, 3-hexenoic acid, 4-heptenoic acid, and 5-hexenoic acid; vinyl carboxyalkyl ethers having 3 to 6 carbon atoms, such as vinyl carboxymethyl ether and vinyl carboxyethyl ether; carboxyalkyl (meth)acrylates having 5 to 12 carbon atoms, such as carboxyethyl acrylate of acryloyloxyethyl succinate and 2-carboxyethyl methacrylate; (meth)acryloyloxyalkyl dicarboxylic acid esters having 7 to 16 carbon atoms, such as acryloyloxyethyl succinate, acryloyloxypropyl succinate, methacryloyloxyethyl succinate, acryloyloxyethyl phthalate, and methacryloyloxyethyl phthalate; and salts thereof.

[0059] Among the monomers (3), at least one selected from the group consisting of (meth)acrylic acid, 3-butenoic acid, 4-pentenoic acid, 2-carboxyethyl acrylate, hydroxyethyl acrylate, 2-hydroxypropyl acrylate, acryloyloxyethyl succinic acid, and salts thereof is preferred, with (meth)acrylic acid being more preferred.

[0060] The content of polar group-containing monomer units in the above polymer is preferably 0.001 to 3.0 mol%, more preferably 2.0 mol% or less, more preferably 0.10 mol% or more, and even more preferably 0.50 mol% or more, relative to the total monomer units.

[0061] As for polymers, in particular, Trifluoroethylene homopolymer, Trifluoroethylene / TFE copolymer, Trifluoroethylene / TFE / HFP copolymer, Trifluoroethylene / TFE / 2,3,3,3-tetrafluoropropene copolymer, Trifluoroethylene / TFE / CTFE copolymer, Trifluoroethylene / TFE / (meth)acrylic acid copolymer, Trifluoroethylene / TFE / 3-butenic acid copolymer, Trifluoroethylene / TFE / 4-pentenoic acid copolymer, Trifluoroethylene / TFE / 2-carboxyethyl acrylate copolymer, Trifluoroethylene / TFE / acryloyloxyethyl succinate copolymer, Trifluoroethylene / TFE / HFP / (meth)acrylic acid copolymer These are some examples.

[0062] In this disclosure, the composition of the polymer is, for example, 19 It can be measured by 1F-NMR. Furthermore, if the polymer contains polar group-containing monomer units as other monomer units, the content of these polar group-containing monomer units can be measured, for example, by acid-base titration of the acid group if the polar group is an acidic group such as a carboxylic acid.

[0063] The weight-average molecular weight (in polystyrene equivalent) of the polymer is preferably 10,000 to 3,000,000, more preferably 30,000 or more, even more preferably 50,000 or more, particularly preferably 200,000 or more, more preferably 2,400,000 or less, even more preferably 2,200,000 or less, and particularly preferably 2,000,000 or less. The above weight-average molecular weight can be measured by gel permeation chromatography (GPC) using dimethylformamide as the solvent.

[0064] The number-average molecular weight (in polystyrene terms) of the polymer is preferably 7,000 to 1,500,000, more preferably 21,000 or more, even more preferably 35,000 or more, more preferably 1,400,000 or less, even more preferably 1,200,000 or less, and particularly preferably 1,100,000 or less. The above number-average molecular weight can be measured by gel permeation chromatography (GPC) using dimethylformamide as the solvent.

[0065] The solution viscosity of the polymer is preferably 10 to 4000 mPa·s, more preferably 50 mPa·s or more, even more preferably 100 mPa·s or more, particularly preferably 150 mPa·s or more, more preferably 3000 mPa·s or less, even more preferably 2000 mPa·s or less, particularly preferably 1500 mPa·s or less, and most preferably 700 mPa·s or less. The solution viscosity is the viscosity of an N-methyl-2-pyrrolidone (NMP) solution containing 5% by mass of the polymer. The viscosity of the NMP solution can be measured at 25°C using a B-type viscometer.

[0066] The melting point of the polymer is preferably 100 to 245°C, more preferably 150°C or higher, even more preferably 180°C or higher, and particularly preferably 195°C or higher. The melting point of the polymer can be determined using a differential scanning calorimetry (DSC) device, by raising the temperature from 30°C to 300°C at a rate of 10°C / min, then lowering it to 30°C at a rate of 10°C / min, and then raising it again to 300°C at a rate of 10°C / min, and taking the temperature at the point of maximum value on the heat of fusion curve.

[0067] The polymer content in the composition is preferably 0.1 to 20% by mass, more preferably 1 to 15% by mass, and even more preferably 3 to 12% by mass, relative to the mass of the composition.

[0068] The polymer can be suitably produced by a method of polymerizing trifluoroethylene and, if necessary, other monomers in a reactor.

[0069] While polymerization methods such as suspension polymerization, emulsion polymerization, and solution polymerization can be employed, suspension polymerization and emulsion polymerization are preferred due to the ease of post-processing and other factors.

[0070] The polymerization temperature is not particularly limited, but from the viewpoint of polymerization rate and the cost required for temperature control, it is preferably 0 to 95°C, and more preferably 15 to 95°C. In particular, the polymerization temperature in suspension polymerization is preferably 15 to 45°C. In particular, the polymerization temperature in emulsion polymerization is 55 to 95°C.

[0071] The polymerization pressure is not particularly limited, but from the viewpoint of polymerization rate and reactor pressure resistance, it is preferably 0.3 to 1 MPaG, more preferably 0.4 MPaG or higher, and more preferably 0.8 MPaG or lower.

[0072] In the polymerization described above, polymerization initiators, surfactants, chain transfer agents, and solvents can be used, and conventionally known ones can be used. As the polymerization initiator, oil-soluble radical polymerization initiators or water-soluble radical polymerization initiators can be used.

[0073] The oil-soluble radical polymerization initiator may be a known oil-soluble peroxide, for example, Dialkyl peroxycarbonates such as dinormal propyl peroxydicarbonate, diisopropyl peroxydicarbonate, and disec-butyl peroxydicarbonate; Peroxy esters such as t-butyl peroxyisobutyrate, t-butyl peroxypivalate, t-hexyl peroxy 2-ethylhexanoate, t-butyl peroxy-2-ethylhexanoate, 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate, and t-amyl peroxypivalate; Dialkyl peroxides such as di-t-butyl peroxide; Di[fluoro(or fluorochloro)acyl]peroxides; These are some typical examples.

[0074] Examples of di[fluoro(or fluorochloro)acyl]peroxides include diacylperoxides represented as [(RfCOO)-]2 (where Rf is a perfluoroalkyl group, an ω-hydroperfluoroalkyl group, or a fluorochloroalkyl group).

[0075] Examples of di[fluoro(or fluorochloro)acyl]peroxides include di(ω-hydroperfluorohexanoyl)peroxide, di(ω-hydro-dodecafluoroheptanoyl)peroxide, di(ω-hydro-tetradecafluorooctanoyl)peroxide, di(ω-hydro-hexadecafluorononanoyl)peroxide, di(perfluorobutyryl)peroxide, di(perfluoropareryl)peroxide, di(perfluorohexanoyl)peroxide, di(perfluoroheptanoyl)peroxide, di(perfluorooctanoyl)peroxide, di(perfluorononanoyl)peroxide, di(ω-chloro-hexafluorobutyryl)peroxide, and di(ω-chloro-decafluoro Examples include hexanoyl peroxide, di(ω-chlorotetradecafluorooctanoyl) peroxide, ω-hydro-dodecafluoroheptanoyl-ω-hydrohexadecafluorononanoyl peroxide, ω-chloro-hexafluorobutyryl-ω-chloro-decafluorohexanoyl peroxide, ω-hydrododecafluoroheptanoyl-perfluorobutyryl peroxide, di(dichloropentafluorobutanoyl) peroxide, di(trichlorooctafluorohexanoyl) peroxide, di(tetrachloroundafluorooctanoyl) peroxide, di(pentachlorotetradecafluorodecanoyl) peroxide, and di(undachlorotriacontafluorodocosanoyl) peroxide.

[0076] The water-soluble radical polymerization initiator may be a known water-soluble peroxide, such as ammonium salts, potassium salts, and sodium salts of persulfuric acid, perboric acid, perchloric acid, superphosphate, and percarbonate; organic peroxides such as disuccinate peroxide and diglutaric acid peroxide; t-butyl permalate; and t-butyl hydroperoxide. A reducing agent such as sulfites may also be used in combination with the peroxide, and the amount used may be 0.1 to 20 times the amount of the peroxide.

[0077] Preferred polymerization methods include suspension polymerization in the presence of a peroxide polymerization initiator and emulsion polymerization in the presence of a redox polymerization initiator. Examples of peroxide polymerization initiators include the oil-soluble peroxides mentioned above. Examples of redox polymerization initiators include combinations of the peroxides mentioned above and reducing agents.

[0078] As the surfactant, known surfactants can be used, such as nonionic surfactants, anionic surfactants, and cationic surfactants. Among these, fluorine-containing anionic surfactants are preferred, and linear or branched fluorine-containing anionic surfactants having 4 to 20 carbon atoms, which may contain ether bonds (i.e., oxygen atoms may be inserted between carbon atoms), are more preferred. The amount of surfactant added (relative to the solvent) is preferably 50 to 5000 ppm.

[0079] By polymerizing in the presence of a chain transfer agent, the solution viscosity, weight-average molecular weight, and other properties of the resulting polymer can be appropriately adjusted. Examples of chain transfer agents include hydrocarbons such as ethane, isopentane, n-hexane, and cyclohexane; aromatics such as toluene and xylene; ketones such as acetone; acetic acid esters such as ethyl acetate and butyl acetate; alcohols such as methanol and ethanol; mercaptans such as methyl mercaptan; and halogenated hydrocarbons such as carbon tetrachloride, chloroform, methylene chloride, and methyl chloride.

[0080] The amount of chain transfer agent added can vary depending on the magnitude of the chain transfer constant of the chain transfer agent, but it is usually 0.01 to 20% by mass relative to the solvent.

[0081] Examples of solvents include water, and mixed solvents of water and alcohol.

[0082] For polymerization such as suspension polymerization, a fluorine-based solvent may be used in addition to water. Examples of fluorine-based solvents include hydrochlorofluoroalkanes such as CH3CClF2, CH3CCl2F, CF3CF2CCl2H, and CF2ClCF2CFHCl; chlorofluoroalkanes such as CF2ClCFClCF2CF3 and CF3CFClCFClCF3; perfluorocyclobutanes such as CF3CF2CF2CF3, CF3CF2CF2CF2CF3, and CF3CF2CF2CF2CF2CF3; CF2HCF2CF2CF2H, CF3CFHCF2CF2CF3, CF3CF2CF2CF2CF2H, CF3CF2CF2CF2CF2H, CF2HCFHCF2CF2CF3, and CF3CF2CF2CF2CF2C Examples include hydrofluorocarbons such as F2H, CF3CH(CF3)CF3CF2CF3, CF3CF(CF3)CFHCF2CF3, CF3CF(CF3)CFHCFHCF3, CF3CH(CF3)CFHCF2CF3, CF2HCF2CF2CF2CF2CF2CF2H, CF3CF2CF2CF2CH2CH3, and CF3CH2CF2CH3; (perfluoroalkyl)alkyl ethers such as F(CF2)4OCH3, F(CF2)4OC2H5, (CF3)2CFOCH3, and F(CF2)3OCH3; and hydrofluoroalkyl ethers such as CF3CH2OCF2CHF2, CHF2CF2CH2OCF2CHF2, and CF3CF2CH2OCF2CHF2, with perfluoroalkanes being preferred. The amount of fluorinated solvent used is preferably 10 to 100% by mass relative to the solvent, from the viewpoint of suspension and economy.

[0083] In suspension polymerization, suspending agents such as methylcellulose, methoxylated methylcellulose, propoxylated methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, polyvinyl alcohol, polyethylene oxide, and gelatin can be used. The amount of suspending agent added (relative to the solvent) is preferably 0.005 to 1.0% by mass, more preferably 0.01 to 0.4% by mass.

[0084] Examples of polymerization initiators used in suspension polymerization include diisopropyl peroxydicarbonate, dinormalpropyl peroxydicarbonate, dinormalheptafluoropropyl peroxydicarbonate, di(secondary butyl)peroxycarbonate, isobutyryl peroxide, di(chlorofluoroacyl)peroxide, di(perfluoroacyl)peroxide, t-butyl peroxypivalate, and t-amyl peroxypivalate. The amount used is preferably 0.1 to 5% by mass relative to the total amount of monomers. By adjusting the amount of polymerization initiator added, the solution viscosity and weight-average molecular weight of the resulting polymer can be appropriately adjusted.

[0085] In suspension polymerization, the degree of polymerization of the resulting polymer may be adjusted by adding chain transfer agents such as ethyl acetate, methyl acetate, acetone, methanol, ethanol, n-propanol, acetaldehyde, propylaldehyde, ethyl propionate, and carbon tetrachloride. The amount used is usually 0.1 to 5% by mass, preferably 0.5 to 3% by mass, relative to the total amount of monomers. By adjusting the amount of chain transfer agent added, the solution viscosity, weight-average molecular weight, etc., of the resulting polymer can be appropriately adjusted.

[0086] The total amount of monomers used is such that the mass ratio of total monomers to water is 1:1 to 1:10, preferably 1:1 to 1:5.

[0087] If an aqueous dispersion containing the polymer is obtained after polymerization, the polymer can be recovered by coagulating, washing, and drying the dispersion. Alternatively, if the polymer is obtained as a slurry, the slurry can be removed from the reactor, washed, and dried to recover the polymer. Drying allows the polymer to be recovered in powder form.

[0088] (solvent) The compositions of this disclosure preferably further contain a solvent.

[0089] Examples of solvents include water or non-aqueous solvents. Examples of non-aqueous solvents include nitrogen-containing organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and dimethylformamide; ketone solvents such as acetone, methyl ethyl ketone, cyclohexanone, and methyl isobutyl ketone; ester solvents such as ethyl acetate and butyl acetate; ether solvents such as tetrahydrofuran and dioxane; and general-purpose low-boiling organic solvents such as mixtures thereof. The polymers used in the compositions of this disclosure exhibit good solubility in these solvents, making the compositions of this disclosure easy to prepare. Furthermore, the resulting compositions have a suitable viscosity.

[0090] Furthermore, at least one solvent selected from the group consisting of esters (1) represented by general formula (1) and ketones (2) represented by general formula (2) may also be used.

[0091] General formula (1): [ka] (In the formula, R 1 and R 2 These are independently H, C1~C 10 A linear or branched aliphatic group, or C6~C 10 It is the aromatic group of [the compound].

[0092] General formula (2): [ka] (In the formula, R 3 and R 4 These are independently H, C1~C 10 A linear or branched aliphatic group, or C6~C 10 It is the aromatic group of [the compound].

[0093] R in general formula (1) 1 and R 2 These are independently H, C1~C 10 A linear or branched aliphatic group, or C6~C 10It is an aromatic group.

[0094] R 1 The number of carbon atoms in the aliphatic group is 1 to 10, preferably 2 or more, more preferably 3 or more, preferably 7 or less, and more preferably 5 or less. 1 An alkyl group is preferred as the aliphatic group. The alkyl group may be linear or branched.

[0095] R 1 The aromatic group has 6 to 10 carbon atoms. The hydrogen atoms bonded to the carbon atoms of the aromatic ring of the aromatic group may or may not be substituted. Examples of substituents include alkyl groups such as methyl groups, and halo groups such as chlorine atoms. 1 The aromatic group is preferably a phenyl group or a benzyl group.

[0096] R 1 For example, C1~C 10 Linear or branched aliphatic groups are preferred, C1-C 10 Linear or branched alkyl groups or C2-C 10 Linear or branched alkenyl groups are more preferred, with methyl, ethyl, propyl, vinyl, isopropenyl, butyl, or pentyl groups being preferred, and propyl, butyl, or pentyl groups being more preferred. These groups may be linear or branched, but linear is preferred.

[0097] R 2 The number of carbon atoms in the aliphatic group is 1 to 10, preferably 3 or more, more preferably 4 or more, preferably 8 or less, and more preferably 6 or less. 2 An alkyl group is preferred as the aliphatic group. The alkyl group may be linear or branched.

[0098] R 2The aromatic group has 6 to 10 carbon atoms. The hydrogen atom bonded to the carbon atom of the aromatic ring of the aromatic group may or may not be substituted. Examples of the substituent include an alkyl group such as a methyl group and a halo group such as a chlorine atom. R 2 As the aromatic group of R

[0099] R 2 is preferably a linear or branched aliphatic group having C1 to C 10 more preferably a linear or branched alkyl group having C1 to C 10 preferably a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group or a hexyl group, and more preferably a butyl group, a pentyl group or a hexyl group. These groups may be linear or branched, but are preferably linear.

[0100] As the ester (1) represented by the general formula (1), at least one selected from the group consisting of ethyl acetate, ethyl butyrate, butyl methacrylate, propyl propionate, ethyl butyrate, butyl butyrate, butyl pentanoate, butyl hexanoate, pentyl butyrate, pentyl pentanoate, pentyl hexanoate, hexyl butyrate, hexyl pentanoate and hexyl hexanoate is preferable, and butyl butyrate is more preferable.

[0101] In the general formula (2), R 3 and R 4 are independently H, a linear or branched aliphatic group having C1 to C 10 or an aromatic group having C6 to C 10

[0102] R 3 and R 4 The aliphatic group has 1 to 10 carbon atoms, preferably 3 or less, and more preferably 2 or less. As the aliphatic group of R 3 an alkyl group is preferable. The alkyl group may be linear or branched.

[0103] R​3 and R 4 The aromatic groups of and R have 6 to 4 carbon atoms. The hydrogen atoms bonded to the carbon atoms of the aromatic ring of the aromatic group may or may not be substituted. Examples of the substituent include an alkyl group such as a methyl group and a halo group such as a chlorine atom. R 3 and R 4 As the aromatic groups of and R, a phenyl group or a benzyl group is preferred.

[0104] R 3 and R 4 As and R, a linear or branched aliphatic group of C1 to C 10 is preferred, a linear or branched alkyl group of C1 to C 10 is more preferred, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group or a hexyl group is preferred, and a methyl group or an ethyl group is more preferred. These groups may be either linear or branched, but a linear structure is preferred.

[0105] As the ketone (2) represented by the general formula (2), at least one selected from the group consisting of acetone and methyl ethyl ketone is preferred.

[0106] Among others, the composition of the present disclosure preferably contains a non-aqueous solvent from the viewpoints of excellent stability and coating properties of the composition, and preferably contains at least one selected from the group consisting of N-methyl-2-pyrrolidone, N,N-dimethylacetamide, dimethylformamide, dimethyl sulfoxide, acetone and methyl ethyl ketone, and more preferably contains N-methyl-2-pyrrolidone.

[0107] (Other components) The composition of the present disclosure may contain other components than the polymer. Examples of the other components include inorganic particles and organic particles. In one embodiment of the composition of the present disclosure, inorganic particles are contained. In one embodiment of the composition of the present disclosure, inorganic particles and organic particles are contained.

[0108] ​​​​As the inorganic particles, at least one selected from the group consisting of metal oxide particles and metal hydroxide particles is preferred. By including inorganic particles in the composition of this disclosure, the heat shrinkage resistance of the separator can be further improved.

[0109] The ratio of polymer to inorganic particles is preferably 50:50 to 1:99 by mass ratio ((polymer):(inorganic particles)), more preferably 30:70 to 2:98, and even more preferably 20:80 to 3:97.

[0110] The average particle size of the inorganic particles is preferably 25 μm or less, more preferably 10 μm or less, even more preferably 5 μm or less, particularly preferably 1 μm or less, and preferably 0.02 μm or more. The average particle size of the inorganic particles is a value obtained by measuring with a transmission electron microscope, a laser particle size distribution analyzer, or the like.

[0111] As metal oxide particles, metal oxides other than alkali metals and alkaline earth metals are preferred from the viewpoint of improving the ion conductivity and shutdown effect of the separator, and at least one selected from the group consisting of aluminum oxide, silicon oxide, titanium oxide, vanadium oxide, and copper oxide is more preferred.

[0112] The average particle size of the metal oxide particles is preferably 25 μm or less, more preferably 10 μm or less, even more preferably 5 μm or less, particularly preferably 1 μm or less, and preferably 0.02 μm or more. The average particle size of the metal oxide particles is a value obtained by measurement using a transmission electron microscope.

[0113] Particularly preferred metal oxide particles are aluminum oxide particles or silicon oxide particles with an average particle diameter of 5 μm or less, due to their excellent ionic conductivity.

[0114] As for the metal hydroxide particles, from the viewpoint of improving the ion conductivity and shutdown effect of the separator, at least one selected from the group consisting of magnesium hydroxide, calcium hydroxide, aluminum hydroxide, chromium hydroxide, zirconium hydroxide, and nickel hydroxide is preferred.

[0115] The average particle size of the metal hydroxide particles is preferably 25 μm or less, more preferably 10 μm or less, even more preferably 5 μm or less, particularly preferably 1 μm or less, and preferably 0.02 μm or more. The average particle size of the metal hydroxide particles is a value obtained by measurement using a transmission electron microscope.

[0116] As for the organic particles, non-conductive crosslinked polymers are preferred, and crosslinked polystyrene, crosslinked polymethacrylate, and crosslinked acrylate are more preferred.

[0117] The ratio of polymer to organic particles is preferably 51:49 to 98:2 by mass ratio ((polymer):(organic particles)), and more preferably 65:35 to 95:5.

[0118] The average particle size of the organic particles is preferably 25 μm or less, more preferably 10 μm or less, even more preferably 5 μm or less, particularly preferably 1 μm or less, and preferably 0.02 μm or more. The average particle size of the organic particles is a value obtained by measurement using a transmission electron microscope.

[0119] The composition may also contain other polymers such as polyacrylate, polymethacrylate, polyacrylonitrile, polyamide-imide, acrylic rubber, carboxyalkylcellulose, alkylcellulose, and hydroxyalkylcellulose.

[0120] (Separator for electrochemical devices) By using the composition of this disclosure, a separator for electrochemical devices can be manufactured. The separator for electrochemical devices of this disclosure comprises a substrate and a coating layer formed from the above composition.

[0121] The substrate and the coating layer may be directly bonded or bonded via another layer, but it is preferable that the coating layer be formed directly on the substrate. The coating layer may be provided on only one side of the substrate or on both sides. Furthermore, the coating layer may be provided so as to cover the entire substrate on which the coating layer is provided, or so as to cover only a part of it.

[0122] The weight of the coating layer, when formed on only one side of the substrate, should be 0.5 to 50.0 g / m², from the viewpoint of adhesion to the electrode and ionic conductivity. 2 The range is preferred. When forming coating layers on both sides of the substrate, the weight of the coating layer is 0.1 to 6.0 g / m². 2 It is preferable.

[0123] The thickness of the coating layer is preferably 1 to 5 μm, more preferably 1 to 4 μm, and even more preferably 1 to 3 μm. When the thickness of the coating layer is within the above range, film break strength and insulation properties can be ensured, and the curling of the substrate is less likely to become excessive.

[0124] As the substrate, a porous substrate having voids or cavities inside is preferred. Examples of porous substrates include microporous membranes, porous sheets made of fibrous materials such as nonwoven fabrics or paper-like sheets, or composite coating layers in which one or more other porous layers are laminated onto these microporous membranes or porous sheets. A microporous membrane refers to a membrane having a large number of fine pores inside, in which these fine pores are interconnected, allowing gas or liquid to pass from one side to the other.

[0125] The materials constituting the base material can be either electrically insulating organic or inorganic materials. In particular, from the viewpoint of providing the base material with a shutdown function, it is preferable to use an organic material as the constituent material of the base material, more preferably a thermoplastic resin, and even more preferably at least one selected from the group consisting of polyethylene, polypropylene, polyimide, polyamide, polyamideimide, polyethylene terephthalate, polyester, and polyacetal.

[0126] The shutdown function refers to a function that prevents thermal runaway of the battery by blocking ion movement when the battery temperature rises, by melting the thermoplastic resin and blocking the pores in the substrate. Suitable thermoplastic resins have a melting point of less than 200°C, and polyolefins are particularly preferred.

[0127] A polyolefin microporous membrane is preferred as the substrate using polyolefin. As the polyolefin microporous membrane, a conventional polyolefin microporous membrane used in separators for non-aqueous secondary batteries, possessing sufficient mechanical properties and ion permeability, can be used. Furthermore, from the viewpoint of having the aforementioned shutdown function, the polyolefin microporous membrane preferably contains polyethylene.

[0128] Polyolefins with a weight-average molecular weight of 100,000 to 5,000,000 are preferable. If the weight-average molecular weight is less than 100,000, it may be difficult to ensure sufficient mechanical properties. If it is greater than 5,000,000, the shutdown characteristics may deteriorate or molding may become difficult.

[0129] Such polyolefin microporous membranes can be manufactured by, for example, the following methods: (i) extruding molten polyolefin resin from a T-die to form a sheet, (ii) subjecting the sheet to a crystallization treatment, (iii) stretching the sheet, and (iv) heat-treating the sheet in sequence to form a microporous membrane. Another method involves (i) melting polyolefin resin together with a plasticizer such as liquid paraffin, extruding it from a T-die, and cooling it to form a sheet, (ii) stretching the sheet, (iii) extracting the plasticizer from the sheet, and (iv) heat-treating the sheet in sequence to form a microporous membrane.

[0130] As porous sheets made of fibrous materials, porous sheets can be made of fibrous materials made of polyester such as polyethylene terephthalate, polyolefins such as polyethylene and polypropylene, heat-resistant polymers such as aromatic polyamides and polyimides, polyethersulfones, polysulfones, polyetherketones, and polyetherimides, or mixtures thereof.

[0131] The base material may be a composite base material in which a functional layer is further laminated. A composite base material is preferable in that it allows for the addition of further functionality by the functional layer. As for the functional layer, for example, from the viewpoint of providing heat resistance, a porous layer made of a heat-resistant resin or a porous layer made of a heat-resistant resin and an inorganic filler can be used. Examples of heat-resistant resins include one or more heat-resistant polymers selected from aromatic polyamides, polyimides, polyethersulfones, polysulfones, polyetherketones, and polyetherimides. Suitable inorganic fillers include metal oxides such as alumina and metal hydroxides such as magnesium hydroxide. As for composite formation methods, there are methods such as coating a porous sheet with a functional layer, joining with an adhesive, and heat-pressing.

[0132] As a base material, a porous base material consisting of at least one selected from the group consisting of polyethylene, polypropylene, polyimide, polyamide, polyethylene terephthalate, polyester, and polyacetal is preferred among those mentioned above.

[0133] The film thickness of the substrate is preferably in the range of 5 to 50 μm from the viewpoint of obtaining good mechanical properties and internal resistance. The upper limit of the above film thickness is more preferably 40 μm, and even more preferably 30 μm. The lower limit of the above film thickness is more preferably 10 μm.

[0134] The Gurley value of the substrate is preferably 500 sec / 100cc Air or less, and more preferably 300 sec / 100cc Air or less. Furthermore, a Gurley value of 50 sec / 100cc Air or more is also preferred. The Gurley value is obtained by measurement using a Gurley densometer in accordance with JIS P 8117.

[0135] The porosity of the substrate is preferably 30-70%, and more preferably 35-60%. The porosity is calculated using the following formula. Porosity = (1 - sample mass (g) / (sample density (g / cm³)) 3 ) × sample volume (cm³) 3 ))) × 100 Sample volume (cm³) 3 The dimensions are calculated as 10cm x 10cm x thickness (cm).

[0136] The average pore size of the substrate is preferably 0.01 to 0.5 μm, and more preferably 0.1 to 0.3 μm. The average pore size is determined by applying the BET formula to the specific surface area (m²) of the substrate using the gas adsorption method. 2 Measure the basis weight (g / m²) of the substrate and measure the basis weight (g / m²). 2 ) multiply by the base material 1m 2 The surface area S of the voids per unit area is calculated. Separately, the porosity is used to calculate the surface area S of the substrate per 1 m². 2 The pore volume V per unit area is calculated. Using the obtained value, the average pore diameter d is calculated from the following formula. d = 4·V / S

[0137] When the Gurley value, porosity, and average pore diameter of the substrate are within the above range, a separator with excellent ion permeability can be obtained, resulting in a battery with good charge-discharge characteristics.

[0138] A separator for electrochemical devices can be manufactured by coating the above composition onto a substrate. The coating method is not particularly limited as long as it can cover the surface of the substrate with a coating layer formed from the composition, but for example, one method is to apply the above composition onto the substrate and dry the coating film. More specifically, as a coating method, one is to roll-coat the above composition onto the substrate, one is to dip the substrate into the above composition, and one is to coat the above composition onto the substrate and then immerse it in a suitable solidifying solution. Alternatively, a separator for electrochemical devices may be manufactured by making a film using the above composition and laminating the obtained film and the substrate by a method such as lamination. An example of a method for making a film using the above composition is to cast the above composition onto a film having a smooth surface, such as a polyester film or an aluminum film, and then peel it off.

[0139] The Gurley value of the separator for electrochemical devices is preferably 500 sec / 100cc Air or less, and more preferably 300 sec / 100cc Air or less. Furthermore, a Gurley value of 50 sec / 100cc Air or more is also preferred. The Gurley value is obtained by measurement using a Gurley densometer in accordance with JIS P 8117.

[0140] For separators used in electrochemical devices, the increase in the Gurley value is preferably 140% or less, more preferably 130% or less, and even more preferably 120% or less. The increase in the Gurley value is also preferably 103% or more. The increase in the Gurley value can be calculated using the following formula. Gurley value increase rate (%) = (Gurley value of separator for electrochemical devices / Gurley value of substrate only) × 100

[0141] (Electrochemical devices) The separator for electrochemical devices of this disclosure is applicable to electrochemical devices. The electrochemical device of this disclosure comprises the above-described separator for electrochemical devices.

[0142] Examples of electrochemical devices include batteries such as secondary batteries and capacitors. Batteries may be primary batteries, storage batteries (secondary batteries), or energy storage elements. Batteries may also be non-aqueous electrolyte batteries. Non-aqueous electrolyte batteries include all batteries that have an electrolyte and a power generation element. Examples of non-aqueous electrolyte batteries include lithium-ion primary batteries, lithium-ion secondary batteries, nickel-metal hydride batteries, lithium-ion capacitors, and electric double-layer capacitors.

[0143] The separator for electrochemical devices of this disclosure can constitute a secondary battery together with a positive electrode, a negative electrode, and a non-aqueous electrolyte. Among these secondary batteries, lithium-ion secondary batteries are particularly preferred. A typical configuration when the separator for electrochemical devices of this disclosure is applied to a lithium-ion secondary battery is described below, but the electrochemistry of this disclosure is not limited to these configurations.

[0144] The positive electrode consists of a positive electrode mixture containing a positive electrode active material, which is the material for the positive electrode, and a current collector.

[0145] The positive electrode active material is not particularly limited as long as it is electrochemically capable of intercalating and releasing lithium ions. A material containing lithium and at least one transition metal is preferred, and examples include lithium transition metal composite oxides such as lithium-cobalt composite oxide, lithium-nickel composite oxide, and lithium-manganese composite oxide, as well as lithium-containing transition metal phosphate compounds.

[0146] The positive electrode mixture preferably further includes a binder, a thickener, and a conductive material.

[0147] As a binder, any material can be used as long as it is safe for the solvent and electrolyte used during electrode manufacturing. Examples include polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene, polypropylene, styrene-butadiene rubber, isoprene rubber, butadiene rubber, ethylene-acrylic acid copolymer, and ethylene-methacrylic acid copolymer.

[0148] Examples of thickening agents include carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, starch oxide, starch phosphorylated, and casein.

[0149] Examples of conductive materials for the positive electrode include graphite and carbon materials such as carbon black.

[0150] Suitable materials for the positive electrode current collector include metals such as aluminum, titanium, or tantalum, or alloys thereof. Aluminum or its alloys are particularly preferred.

[0151] The positive electrode can be manufactured by conventional methods. For example, the positive electrode active material can be mixed with the aforementioned binder, thickener, conductive material, solvent, etc., to form a slurry-like positive electrode mixture, which can then be applied to a current collector, dried, and pressed to increase its density.

[0152] The negative electrode consists of a negative electrode mixture containing negative electrode material and a current collector.

[0153] Examples of negative electrode materials include carbonaceous materials capable of intercalating and releasing lithium ions, such as thermal decomposition products of organic materials under various thermal decomposition conditions, artificial graphite, and natural graphite; metal oxide materials capable of intercalating and releasing lithium ions, such as tin oxide and silicon oxide; lithium metal; and various lithium alloys. Two or more of these negative electrode materials may be used in combination.

[0154] Preferred carbonaceous materials capable of intercalating and releasing lithium ions include artificial graphite or refined natural graphite produced by high-temperature treatment of easily graphitizable pitch obtained from various raw materials, or graphite obtained by surface-treating these graphites with pitch or other organic materials and then carbonizing them.

[0155] The negative electrode mixture preferably further includes a binder, a thickener, and a conductive material. Examples of binders include those similar to those used for the positive electrode, as described above. Examples of thickeners include those similar to those used for the positive electrode, as described above. Examples of conductive materials for the negative electrode include metallic materials such as copper and nickel; and carbon materials such as graphite and carbon black.

[0156] Suitable materials for the negative electrode current collector include copper, nickel, and stainless steel. Among these, copper is preferred due to its ease of processing into thin films and its cost-effectiveness.

[0157] The negative electrode can be manufactured using conventional methods. For example, the negative electrode material may be mixed with the aforementioned binder, thickener, conductive material, solvent, etc., to form a slurry, which is then applied to a current collector, dried, and pressed to increase its density.

[0158] As the non-aqueous electrolyte, a known electrolyte salt dissolved in a known organic solvent for dissolving electrolyte salts may be used.

[0159] The organic solvent for dissolving the electrolyte salt is not particularly limited, but one or more of the following can be used: hydrocarbon solvents such as propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and vinylene carbonate; and fluorinated solvents such as fluoroethylene carbonate, fluoroether, and fluorinated carbonate.

[0160] Examples of electrolyte salts include LiClO4, LiAsF6, LiBF4, LiPF6, LiCl, LiBr, CH3SO3Li, CF3SO3Li, LiN(SO2CF3)2, LiN(SO2C2F5)2, and cesium carbonate.

[0161] The concentration of the electrolyte salt is preferably 0.8 mol / liter or higher, and more preferably 1.0 mol / liter or higher. The upper limit depends on the organic solvent used to dissolve the electrolyte salt, but is usually 1.5 mol / liter.

[0162] The shape of a lithium-ion secondary battery can be arbitrary, and examples include cylindrical, prismatic, laminated, coin-type, and large-sized batteries. The shape and configuration of the positive electrode, negative electrode, and separator can be modified according to the shape of each battery.

[0163] (polymer) This disclosure also relates to polymers containing trifluoroethylene units, tetrafluoroethylene units, and monomer (α) units, wherein monomer (α) is at least one selected from the group consisting of fluorinated monomers (excluding trifluoroethylene and tetrafluoroethylene) and polar group-containing monomers. Specific embodiments of this ternary polymer will now be described in detail.

[0164] The polymers of this disclosure may have the same configuration as the polymers contained in the compositions of this disclosure, and it is preferable that they have the same configuration, except that they contain tetrafluoroethylene units and monomer (α) units as essential monomer units in addition to trifluoroethylene units. Therefore, the polymers of this disclosure can be suitably used as polymers included in compositions for coating separators for electrochemical devices.

[0165] Since the polymers of this disclosure contain trifluoroethylene units, tetrafluoroethylene units, and monomer (α) units, when a separator is coated with the polymers of this disclosure, a coating with excellent electrolyte resistance can be formed, and the heat shrinkage resistance of the separator can be improved.

[0166] The content of trifluoroethylene units in the above polymer is preferably 57 to 99 mol%, more preferably 60 mol% or more, even more preferably 62 mol% or more, particularly preferably 65 mol% or more, more preferably 98 mol% or less, even more preferably 97 mol% or less, still more preferably 90 mol% or less, and particularly preferably 80 mol% or less, based on the total monomer units. In the polymer of this disclosure, by setting the content of trifluoroethylene units to 57 to 99 mol%, the solubility of the polymer in solvents such as N-methyl-2-pyrrolidone is significantly improved, and a composition with appropriate viscosity can be obtained. Furthermore, by setting the content of trifluoroethylene units to 65 mol% or more, the heat shrinkage resistance of the separator is further improved.

[0167] The tetrafluoroethylene unit content in the polymer of this disclosure is preferably 1 to 43 mol%, more preferably 40 mol% or less, even more preferably 38 mol% or less, particularly preferably 35 mol% or less, more preferably 2 mol% or more, even more preferably 10 mol% or more, and particularly preferably 20 mol% or more, based on the total monomer units.

[0168] The total content of trifluoroethylene units and tetrafluoroethylene units in the polymer of this disclosure is more preferably 90 to 99.99 mol%, even more preferably 92 mol% or more, particularly preferably 94 mol% or more, even more preferably 99 mol% or less, and particularly preferably 98 mol% or less.

[0169] The monomer (α) unit content in the polymer of this disclosure is more preferably 10 to 0.01 moles, even more preferably 8 mol% or less, particularly preferably 6 mol% or less, even more preferably 1 mol% or more, and particularly preferably 2 mol% or more.

[0170] (Laminated structure) This disclosure also relates to laminates comprising a substrate formed from an organic material and a coating layer formed from a composition. Specific embodiments of the laminates of this disclosure will now be described in detail.

[0171] The laminate of this disclosure may have the same configuration as the separator for electrochemical devices of this disclosure, except that the substrate is limited to being formed from an organic material, and it is preferable that it has the same configuration.

[0172] The laminate of this disclosure can be suitably used as a separator for electrochemical devices.

[0173] The laminate of this disclosure comprises a substrate formed from an organic material and a coating layer formed from the above-described composition. Therefore, since the formation of the coating layer is easy, the laminate of this disclosure can be manufactured with high productivity. Furthermore, the coating layer has high electrolyte resistance, and therefore the coating layer is less likely to dissolve and swell even when in contact with the electrolyte used in lithium-ion secondary batteries. Moreover, the laminate of this disclosure is less likely to shrink even when exposed to high-temperature environments.

[0174] Although embodiments have been described above, it should be understood that various modifications to the form and details are possible without departing from the spirit and scope of the claims. [Examples]

[0175] Next, embodiments of this disclosure will be described with reference to experimental examples, but this disclosure is not limited to such experimental examples.

[0176] Each value in the experimental example was measured using the following method.

[0177] <Monomial composition of polymers> Using an NMR analyzer (Agilent Technologies, VNS400MHz), 19 The monomer composition of polymers was measured using F-NMR in acetone or NMP solution. Polymers insoluble in acetone and NMP were measured using a nuclear magnetic resonance spectrometer AC300 (Bruker-Biospin) at a measurement temperature of the polymer's melting point + 20°C. 19 The values ​​were determined by performing F-NMR measurements and taking the integral values ​​of each peak.

[0178] <Weight average molecular weight> Measurements were taken using gel permeation chromatography (GPC). A Tosoh AS-8010, CO-8020, and column (three GMHHR-H columns connected in series) were used, along with a Shimadzu RID-10A. Dimethylformamide (DMF) was used as the solvent, flowing at a rate of 1.0 ml / min. The data (reference: polystyrene) was used for calculation.

[0179] <Melting point> Using a differential scanning calorimetry (DSC) system, the temperature was increased from 50°C to 300°C at a rate of 10°C / min, then decreased to 30°C at 10°C / min, and then increased again to 300°C at a rate of 10°C / min. The temperature corresponding to the maximum value in the heat of fusion curve was determined as the melting point.

[0180] <Solution viscosity> A polymer NMP solution (5% by mass) was prepared. The viscosity of the NMP solution was measured 10 minutes after the start of measurement using a B-type viscometer (TV-10M, manufactured by Toki Sangyo Co., Ltd.) at 25°C, rotor No. M3, and rotation speed of 30 rpm.

[0181] <Electrolyte resistance> Each polymer was heated to a temperature above its melting point, and sheets with a thickness of 100-150 μm were obtained by hot pressing. A portion of these sheets was immersed in a solution of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 30 / 70 containing 1.0 M LiPF6, and after 5 days at 60°C, the sheet shape was visually inspected and evaluated according to the following criteria. The results are shown in Table 1. ○: The sheet shape was maintained. ×: The sheet shape was not maintained.

[0182] <Separator thermal shrinkage rate> The separators prepared in each experimental example were placed in an oven and heated at 140°C for 30 minutes. The area of ​​the separators was measured before and after heating, and the thermal shrinkage rate was calculated using the following formula. Thermal shrinkage rate (%) = (Area of ​​separator after heating) / (Area of ​​separator before heating) × 100

[0183] <Synthesis Example 1> (Synthesis of trifluoroethylene-tetrafluoroethylene copolymer (polymer a)) In a 300 mL autoclave, 61 g of pure water, 89 g of 1,1,2,2-tetrafluoro-1-(2,2,2-trifluoroethoxy)ethane (HFE-347pc-f), 9.6 g of trifluoroethylene, 0.3 g of tetrafluoroethylene, and 0.3 g of a methanol solution of 50% by mass of dinormal propyl peroxydicarbonate (hereinafter abbreviated as "NPP") as an initiator were charged, and the temperature was raised to 35°C to carry out the polymerization reaction. During the polymerization reaction, a mixed gas of trifluoroethylene and tetrafluoroethylene (molar ratio (trifluoroethylene / tetrafluoroethylene) = 97 / 3) was added to maintain a pressure of 0.35 MPa. When the weight of the added gas reached 9 g, the monomers in the autoclave were purged, and the resulting copolymer (polymer a) was recovered. Polymer a had a trifluoroethylene-based polymerization unit / tetrafluoroethylene-based polymerization unit ratio of 97 / 3 (molar ratio) as measured by NMR, a weight-average molecular weight of 350,000 as measured by GPC, and a melting point of 202°C as measured by DSC.

[0184] <Synthesis Example 2> (Synthesis of trifluoroethylene-tetrafluoroethylene copolymer (polymer b)) 40 g of HFE-347pc-f, 12 g of trifluoroethylene, 2 g of tetrafluoroethylene, and 0.5 g of a perfluorohexane solution of 8% by mass of di(ω-hydro-dodecafluorohexanoyl) peroxide (hereinafter abbreviated as "DHP") as an initiator were charged into a 100 mL autoclave, and the temperature was raised to 25°C to carry out the polymerization reaction. The reaction was allowed to proceed until the pressure decreased from 0.7 MPa to 0.5 MPa, the monomers in the autoclave were purged, and the resulting copolymer (polymer b) was recovered. Polymer b had a trifluoroethylene-based polymerization unit / tetrafluoroethylene-based polymerization unit ratio of 87 / 13 (molar ratio) as measured by NMR, a weight-average molecular weight of 290,000 as measured by GPC, and a melting point of 220°C as measured by DSC.

[0185] <Synthesis Example 3> (Synthesis of trifluoroethylene-tetrafluoroethylene copolymer (polymer c)) A 300 mL autoclave was charged with 61 g of pure water, 89 g of HFE-347pc-f, 7.6 g of trifluoroethylene, 2.7 g of tetrafluoroethylene, and 0.3 g of a 50% by mass methanol solution of NPP as an initiator. The mixture was heated to 35°C, and the polymerization reaction was carried out. During the polymerization reaction, a mixed gas of trifluoroethylene and tetrafluoroethylene (molar ratio (trifluoroethylene / tetrafluoroethylene) = 70 / 30) was added to maintain a pressure of 0.35 MPa. When the weight of the added gas reached 9 g, the monomers in the autoclave were purged, and the resulting copolymer (polymer c) was recovered. Polymer c had a trifluoroethylene-based polymerization unit / tetrafluoroethylene-based polymerization unit ratio of 69 / 31 (molar ratio) as measured by NMR, a weight-average molecular weight of 420,000 as measured by GPC, and a melting point of 239°C as measured by DSC.

[0186] <Synthesis Example 4> (Synthesis of trifluoroethylene-tetrafluoroethylene-hexafluoropropylene copolymer (polymer d)) In a 300 mL autoclave, 61 g of pure water, 89 g of HFE-347pc-f, 7.4 g of trifluoroethylene, 3.0 g of tetrafluoroethylene, 30 g of hexafluoropropylene, and 0.2 g of a 50% by mass methanol solution of NPP as an initiator were charged, and the temperature was raised to 35°C to carry out the polymerization reaction. During the polymerization reaction, a mixed gas of trifluoroethylene, tetrafluoroethylene, and hexafluoropropylene (molar ratio (trifluoroethylene / tetrafluoroethylene / hexafluoropropylene) = 66 / 30 / 4) was added to maintain a pressure of 0.61 MPa. When the weight of the added gas reached 9 g, the monomers in the autoclave were purged, and the resulting copolymer (polymer d) was recovered. Polymer d had a molar ratio of trifluoroethylene-based polymerization units / tetrafluoroethylene-based polymerization units / hexafluoropropylene-based polymerization units of 62 / 33 / 5, as measured by NMR. Its weight-average molecular weight, as measured by GPC, was 300,000, and its melting point, as measured by DSC, was 198°C.

[0187] <Synthesis Example 5> (Synthesis of trifluoroethylene-tetrafluoroethylene-hexafluoropropylene copolymer (polymer e)) 61 g of pure water, 89 g of HFE-347pc-f, 7.6 g of trifluoroethylene, 2.7 g of tetrafluoroethylene, 18 g of hexafluoropropylene, and 0.5 g of a methanol solution of 50% by mass of NPP as an initiator were charged into a 300 mL autoclave, and the temperature was raised to 35°C to carry out the polymerization reaction. During the polymerization reaction, a mixed gas of trifluoroethylene, tetrafluoroethylene, and hexafluoropropylene (molar ratio (trifluoroethylene / tetrafluoroethylene / hexafluoropropylene) = 70 / 28 / 2) was added to maintain a pressure of 0.45 MPa. When the weight of the added gas reached 9 g, the monomers in the autoclave were purged, and the resulting copolymer (polymer e) was recovered. Polymer e had a molar ratio of trifluoroethylene-based polymerization units / tetrafluoroethylene-based polymerization units / hexafluoropropylene-based polymerization units of 67 / 31 / 2, as measured by NMR. Its weight-average molecular weight, as measured by GPC, was 340,000, and its melting point, as measured by DSC, was 225°C.

[0188] <Synthesis Example 6> Synthesis of trifluoroethylene-tetrafluoroethylene-2,3,3,3-tetrafluoropropene copolymer (polymer f)) In a 300 mL autoclave, 61 g of pure water, 89 g of HFE-347pc-f, 7.4 g of trifluoroethylene, 3.0 g of tetrafluoroethylene, 0.2 g of 2,3,3,3-tetrafluoropropene, and 0.2 g of a 50% by mass methanol solution of NPP as an initiator were charged, and the temperature was raised to 35°C to carry out the polymerization reaction. During the polymerization reaction, a mixed gas of trifluoroethylene, tetrafluoroethylene, and 2,3,3,3-tetrafluoropropene (molar ratio (trifluoroethylene / tetrafluoroethylene / 2,3,3,3-tetrafluoropropene) = 73 / 26 / 1) was added to maintain a pressure of 0.35 MPa. When the weight of the added gas reached 9 g, the monomers in the autoclave were purged, and the resulting copolymer (polymer f) was recovered. Polymer f had a molar ratio of trifluoroethylene-based polymerization units / tetrafluoroethylene-based polymerization units / 2,3,3,3-tetrafluoropropene-based polymerization units of 69 / 29 / 2, measured by NMR. Its weight-average molecular weight, measured by GPC, was 250,000, and its melting point, measured by DSC, was 219°C.

[0189] <Synthesis Example 7> (Synthesis of trifluoroethylene-tetrafluoroethylene-chlorotrifluoroethylene copolymer (polymer g)) In a 300 mL autoclave, 61 g of pure water, 89 g of HFE-347pc-f, 7.4 g of trifluoroethylene, 3.0 g of tetrafluoroethylene, 0.5 g of chlorotrifluoroethylene, and 0.2 g of a methanol solution of 50% by mass of NPP as an initiator were charged, and the temperature was raised to 35°C to carry out the polymerization reaction. During the polymerization reaction, a mixed gas of trifluoroethylene, tetrafluoroethylene, and chlorotrifluoroethylene (molar ratio (trifluoroethylene / tetrafluoroethylene / chlorotrifluoroethylene) = 67 / 31 / 2) was added to maintain a pressure of 0.33 MPa. When the weight of the added gas reached 9 g, the monomers in the autoclave were purged, and the resulting copolymer (polymer g) was recovered. Polymer g had a molar ratio of trifluoroethylene-based polymerization units / tetrafluoroethylene-based polymerization units / chlorotrifluoroethylene-based polymerization units of 65 / 33 / 2, as measured by NMR. Its weight-average molecular weight, as measured by GPC, was 450,000, and its melting point, as measured by DSC, was 226°C.

[0190] <Synthesis Example 8> (Synthesis of trifluoroethylene-vinylidene fluoride copolymer (polymer h)) In a 3L autoclave, 1000g of water, 500g of R-113, 5g of an 8% by mass perfluorohexane solution of DHP as an initiator, 1g of n-pentane, and a mixed gas of trifluoroethylene and vinylidene fluoride (molar ratio (trifluoroethylene / vinylidene fluoride) = 60 / 40) were added until the pressure reached 0.54 MPaG, and the polymerization reaction was carried out at 20°C. A mixed gas of trifluoroethylene and vinylidene fluoride (molar ratio (trifluoroethylene / vinylidene fluoride) = 54 / 46) was added to maintain the pressure at 0.54 MPaG, and the reaction was continued until the added mixed gas reached 380g. The monomers in the autoclave were purged, and the resulting copolymer (polymer h) was recovered. Polymer h had a trifluoroethylene-based polymerization unit / vinylidene fluoride-based polymerization unit ratio of 54 / 46 (molar ratio) as measured by NMR, a weight-average molecular weight of 900,000 as measured by GPC, and a melting point of 162°C as measured by DSC.

[0191] <Synthesis Example 9> (Synthesis of trifluoroethylene-tetrafluoroethylene copolymer (polymer i)) A 300 mL autoclave was charged with 61 g of pure water, 89 g of HFE-347pc-f, 6.9 g of trifluoroethylene, 3.6 g of tetrafluoroethylene, and 0.2 g of a methanol solution of 50% by mass of NPP as an initiator. The mixture was heated to 35°C, and the polymerization reaction was carried out. During the polymerization reaction, the pressure was reduced from 0.35 MPa to 0.34 MPa. The monomers in the autoclave were purged, and the resulting copolymer (polymer i) was recovered. Polymer i was insoluble in acetone and NMP. The ratio of polymerization units based on trifluoroethylene to polymerization units based on tetrafluoroethylene, as measured by melt NMR, was 55 / 45 (molar ratio), and the melting point, as measured by DSC, was 249°C.

[0192] Experimental Example 1 Polymer a and NMP were mixed to prepare a 6% by mass solution of polymer a with NMP. Additionally, NMP / water was mixed in a 55 / 45 ratio to prepare a phase separation solution. The polymer a NMP solution was applied to both sides of a polyethylene (PE) separator, and the coated separator was immersed in the phase separation solution for 3 minutes. Next, the separator was immersed in water for 3 minutes and dried in an 80°C oven for 30 minutes to produce a polymer-coated separator. The thermal shrinkage rate was measured using the produced separator. The results are shown in Table 1.

[0193] Experimental Examples 2-7 Separators were manufactured using polymers b to g individually, in the same manner as in Experimental Example 1, and their thermal shrinkage rates were measured. The results are shown in Table 1.

[0194] Comparative Examples 1-2 Separators were manufactured using polymers h and i individually, in the same manner as in Experimental Example 1, and their thermal shrinkage rates were measured. The results are shown in Table 1.

[0195] Comparative Example 3 A copolymer of vinylidene fluoride and hexafluoropropylene, with a molecular weight ratio of 93 / 7 (molar ratio) of polymerization units based on vinylidene fluoride and hexafluoropropylene, a weight-average molecular weight of 220,000, and a melting point of 131°C, was used to produce a separator in the same manner as in Experimental Example 1, and the thermal shrinkage rate was measured. The results are shown in Table 1.

[0196] [Table 1]

[0197] The abbreviations in the table represent the following monomers, respectively. 3FH: Trifluoroethylene VdF: Vinylidene fluoride TFE: Tetrafluoroethylene HFP: Hexafluoropropylene CTFE: Chlorotrifluoroethylene 1234yf: 2,3,3,3-tetrafluoropropene

Claims

1. A polymer containing trifluoroethylene units, tetrafluoroethylene units, and monomer (α) units, wherein monomer (α) is at least one selected from the group consisting of fluorinated monomers (excluding trifluoroethylene and tetrafluoroethylene) and polar group-containing monomers, The trifluoroethylene unit content of the polymer is 57 to 99 mol% relative to the total monomer units. A polymer having a tetrafluoroethylene unit content of 1 to 43 mol% relative to the total monomer units.

2. The polymer according to claim 1, wherein the total content of trifluoroethylene units and tetrafluoroethylene units of the polymer is 90 to 99.99 mol% relative to the total monomer units, and the content of monomer (α) units is 10 to 0.01 mol relative to the total monomer units.

3. The polymer according to claim 1 or 2, wherein the monomer (α) is a fluorinated monomer (excluding trifluoroethylene and tetrafluoroethylene).

4. A laminate comprising a substrate formed from a thermoplastic resin and a coating layer formed from a composition, The composition contains a polymer containing trifluoroethylene units and tetrafluoroethylene units, The trifluoroethylene unit content of the polymer is 57 to 99 mol% relative to the total monomer units. The tetrafluoroethylene unit content of the polymer is 1 to 43 mol% relative to the total monomer units. If the polymer contains monomer units other than trifluoroethylene units and tetrafluoroethylene units, the other monomers include at least one monomer (α) selected from the group consisting of fluorinated monomers (excluding trifluoroethylene and tetrafluoroethylene) and polar group-containing monomers. Laminated structure.

5. The laminate according to claim 4, wherein the thermoplastic resin is at least one selected from the group consisting of polyethylene, polypropylene, polyimide, polyamide, polyamideimide, polyethylene terephthalate, polyester, and polyacetal.

6. The laminate according to claim 4 or 5, wherein the laminate is a separator for an electrochemical device.

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